Jet pump

ABSTRACT

A jet pump ( 26 ) includes an elongate tubular housing ( 30 ) that has a longitudinal axis (A), an upstream first end ( 32 ) and a downstream second end ( 34 ). A nozzle assembly ( 50 ) and a mixing tube/diffuser assembly ( 52 ) are removably received within the housing ( 30 ). The housing ( 30 ) includes a first inlet vent ( 40 ) for a HP first fluid, a second inlet vent ( 42 ) for a LP second fluid and an outlet vent ( 48 ) at the downstream second end ( 34 ) of the housing for the combined first and second fluids. The first and second inlet vents ( 40, 42 ) extend non-axially through a circumferential wall ( 31 ) of the tubular housing. The nozzle assembly ( 50 ) and the mixing tube/diffuser assembly ( 52 ) can removed from the housing ( 30 ) through the upstream first end ( 32 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 to British applicationno. GB 1405229.4 filed Mar. 24, 2014, and the disclosure of said Britishapplication is hereby incorporated by reference in its entirety.

FIELD

The present invention relates to a jet pump and in particular, but notexclusively, to a jet pump for use in the oil and gas industries.

BACKGROUND

Jet pumps or eductors are passive devices that use energy from a highpressure (HP) fluid source to boost the pressure of a low pressure (LP)fluid. The terms jet pump, eductor, ejector and gas jet compressor areused in various industries and refer to the same general type of device.The HP and LP fluids may each consist of liquids, gases or a mixture ofliquids and gases.

FIGS. 1 and 2 show the key features of a typical jet pump. HP fluid froma HP source passes through a HP inlet 4 to a jet pump 6, where it passesthrough constriction known as a nozzle assembly 8 that increases thevelocity of the fluid. In this way part of the potential (pressure)energy of the HP fluid is converted to kinetic energy (high velocityfluid). As a result, the pressure of the fluid in a nozzle dischargezone 10 in front of the nozzle assembly 8 drops significantly.

LP fluid from a LP source passes through a LP inlet 12 and is introducedinto the jet pump at the nozzle discharge zone 10, where it is entrainedin the flow of fluid emerging from the nozzle assembly 8. The mixture offluids then passes through a mixing tube 14 where momentum and energyare exchanged between the fluids. The mixture finally passes through anexpanding diffuser 16 where the velocity of flow normalises and pressurerecovery takes place. The pressure at the outlet 18 of the jet pump willbe at an intermediate value between the pressures of the HP and LPfluids at the inlets 4, 12.

Jet pumps have been used successfully in a variety of applicationsonshore or near the bottom of oil or gas wells. In such situations theHP fluid may be gas or a high pressure liquid such as oil or water. TheLP fluid could be gas, or liquid (oil and/or water), or a mixture of gasand liquid.

For maximum efficiency, the dimensions of the nozzle assembly 8 and themixing tube/diffuser assembly 14, 16 must be selected according to thepressures, flow rates and types of fluids delivered to the jet pump. Insome jet pumps the nozzle 8 and the mixing tube/diffuser 14, 16 comprisereplaceable components that are mounted within a housing 20. This allowsthe internal components 8, 14, 16 to be removed and exchanged if theoperating conditions change.

In most jet pumps used for onshore or offshore applications the HP inlet4 is in line with axis of the jet pump as shown in FIGS. 1 and 2, whilstthe LP inlet 12 comprises a Tee junction 12, such that the LP inlet isat 90 degrees to the longitudinal axis A of the jet pump. In otherwords, the jet pump has an axial HP inlet 4, an axial outlet 18 and anon-axial LP inlet 12. The nozzle assembly 8 can be introduced into thejet pump through the HP inlet 4 at one end of the housing 20. There isalso a patented jet pump system (GB2384027B) that enables the nozzleassembly 8 to be removed and replaced through the HP inlet end 4 of thejet pump, while the mixing tube/diffuser section 14, 16 can be removedand replaced through the outlet end 18 of the jet pump.

When the jet pump is in operation and removal and replacement of theinternal components is needed, a spool piece comprising a flanged lengthof pipe (not shown) must be removed from both the HP inlet end 4 and theoutlet end 18 of the jet pump to provide access to the internalcomponents. Sufficient space must be available at both ends of the jetpump to allow the nozzle assembly 8 and the mixing tube/diffuserassembly 14, 16 to be pulled out of the housing 20. This operation istime consuming and requires re-installing the spool pieces after theinstallation of the new internal components, followed by tightening thebolts at both HP inlet and outlet ends 4, 18 and checking the system forleaks.

SUMMARY

It is an object of the present invention to provide a jet pump thatmitigates one or more of the aforesaid disadvantages.

According to one aspect of the present invention there is provided a jetpump including an elongate tubular housing that has a longitudinal axis,an upstream first end and a downstream second end, a nozzle assembly anda mixing tube/diffuser assembly, said nozzle assembly and said mixingtube/diffuser assembly being removably received within the housing, afirst inlet vent for a HP first fluid, a second inlet vent for a LPsecond fluid and an outlet vent at the downstream second end of thehousing for the combined first and second fluids, wherein the first andsecond inlet vents extend non-axially through a circumferential wall ofthe tubular housing, and wherein the nozzle assembly and the mixingtube/diffuser assembly can removed from the housing through the upstreamfirst end thereof.

The configuration of the jet pump makes it possible to remove the nozzleassembly and the mixing tube/diffuser assembly through the upstreamfirst end of the housing without disconnecting the HP and LP feed linesfrom the jet pump. The internal components of the jet pump can thereforebe removed and replaced relatively quickly and easily, thus enabling thejet pump to be adapted readily to different operating conditions toensure that it operates efficiently.

Advantageously, one or both of the first and second inlet vents extendthrough a circumferential wall of the tubular housing at an angle θrelative to the longitudinal axis, where 0°<θ≦90°. The first and secondinlet vents may extend through the circumferential wall of the tubularhousing at an angle of 90° relative to the longitudinal axis.Alternatively, they may extend through the circumferential wall of thetubular housing at an acute angle relative to the longitudinal axis sothat the HP and LP fluids entering the housing have a component ofvelocity in the direction of flow through the housing.

Advantageously, the jet pump includes a removable closure member at theupstream first end of the housing. The removable closure member may forexample comprise a blind flange plate that is removably attached to theupstream first end of the housing in order to seal that end of thehousing hermetically.

Advantageously, the nozzle assembly and the mixing tube/diffuserassembly are interconnected by a link assembly, allowing them to beremoved as a unit from the housing.

Advantageously, the link assembly is configured such that the nozzleassembly and the mixing tube/diffuser assembly are separable. This makesit possible to replace either nozzle assembly or the mixingtube/diffuser assembly, without replacing the other assembly.

Advantageously, the jet pump includes a pull-out assembly connected tothe nozzle assembly for extracting the nozzle assembly and the mixingtube/diffuser assembly from the housing through the upstream first endthereof. This simplifies extraction of the nozzle assembly and themixing tube/diffuser assembly from the housing.

Advantageously, the pull-out assembly is separable from the nozzleassembly. The pull-out assembly and the nozzle assembly may for examplebe interconnected by separable screw threads. This allows the nozzleassembly to be replaced without replacing the pull-out assembly.

Advantageously, the jet pump includes a tubular sleeve element thatinterconnects the pull-out assembly and the nozzle assembly.

Advantageously, the tubular sleeve element includes a fluid flowpassageway configured to allow HP fluid to flow from the first inletvent to the nozzle assembly.

Advantageously, the first inlet vent extends through the circumferentialwall of the tubular housing upstream of the nozzle assembly.

Advantageously, the second inlet vent extends through thecircumferential wall of the tubular housing downstream of the nozzleassembly and upstream of the mixing tube/diffuser assembly. Preferably,the second inlet vent extends through the circumferential wall of thetubular housing in the vicinity of a nozzle discharge zone immediatelydownstream of the nozzle assembly.

According to one preferred aspect of the present invention there isprovided a Tee spool piece 40 for the introduction of the HP fluids.Therefore, unlike conventional jet pumps, the HP fluid entry is also at90 degrees to the longitudinal axis of the jet pump via flange 44. Inthis arrangement access to the internals of the jet pump, which are thenozzle assembly 58 and the mixing tube 52 and diffuser 68, is via aflanged end 36 of the jet pump which is normally closed by the blindflange 49. This arrangement therefore allows the internals to be pulledout of the jet pump from one end which is not connected to HP or LPinlets or the discharge lines and results in not needing to remove spoolpieces attached to the HP inlet and the discharge line of the jet pump.

BRIEF DESCRIPTION OF DRAWINGS

An embodiment of the invention will now be described by way of examplewith reference to the accompanying drawings, in which:

FIG. 1 is a sectional side view of a known jet pump;

FIG. 2 is a sectional isometric view of a known jet pump, and

FIG. 3 is a sectional side view of a jet pump according to an embodimentof the invention.

DETAILED DESCRIPTION

FIG. 3 shows a jet pump 26 according to a first embodiment of theinvention. The jet pump 26 comprises a substantially cylindrical tubularelongate housing 30 having a circumferential wall 31, a first end 32 anda second end 34. A first flange plate 36 is provided at the first end 32of the housing 30 and a second flange plate 38 is provided at thedownstream second end 34 of the housing 30. The housing 30 also includesfirst and second inlet pipes 40, 42, which extend outwards from thehousing substantially perpendicular to the longitudinal axis A of thehousing 30. The first and second inlet pipes 40, 42 are provided attheir outer ends with inlet flange plates 44, 46 respectively andcomprise inlet vents that extend through the circumferential wall 31 ofthe housing 30. The first and second inlet pipes 40, 42 are displacedaxially from one another, the first inlet pipe 40 being located towardsthe first end 32 of the housing 30, while the second inlet pipe 42 islocated towards the middle of the housing 30, midway between the firstand second ends 36, 38. The first and second inlet pipes 40, 42 areconnected in use to HP and LP delivery lines (not shown) to receive HPand LP fluids respectively.

The second end 34 of the housing 30 provides an outlet 48 for fluidsflowing out of the jet pump. The first end 32 of the housing is closedand sealed by a blind flange plate 49, which is bolted to the firstflange plate 36.

A nozzle assembly 50 and a mixing tube/diffuser assembly 52 areremovably mounted within the tubular body of the housing 30. The nozzleassembly 50 includes a tubular cylindrical body 54 having a cylindricalmounting portion 56 at one end and a hollow conical nozzle portion 58 atthe other end, which leads to the nozzle outlet 60. The mounting portion56 carries a pair of O-rings 62 in grooves on its outer surface, whichform a seal with the inner surface of the cylindrical housing 30 andprevent HP fluid from inlet 40 from bypassing the nozzle assembly andflowing directly to the mixing tube/diffuser assembly 52.

The mixing tube/diffuser assembly 52 comprises a tubular body that has asliding fit within the downstream part of the housing 30. The tubularbody has a longitudinal bore that includes a converging upstream portion64, a central mixer portion 66 of constant diameter and a divergingdownstream portion 68. The upstream portion 64, which comprises theinlet to the mixing tube/diffuser assembly 52, is located in thevicinity of the nozzle discharge zone 70, which is just downstream ofthe nozzle 60, to receive fluids discharged from the nozzle 60. Thedownstream end of the mixer tube/diffuser assembly 52 is located closeto the downstream second end 34 of the housing. The mixer tube/diffuserassembly 52 carries a pair of O-rings 72 in grooves on its outersurface, which form a seal with the inner surface of the cylindricalhousing 30.

The nozzle assembly 50 is connected by a tubular cylindrical section 74to an extractor device 76 located towards the first end 32 of thehousing. The extractor device 76 includes a connector piece 78 thatextends axially towards the first end 32 of the housing. When the blindflange plate 49 is removed, the extractor device 76 can be engaged by anextractor tool (not shown) and withdrawn axially from the housing 30through the first end 32, thereby removing the nozzle assembly 50.

The cylindrical section 74 has an opening 80 through which a highpressure first fluid HP can flow from the first inlet pipe 40 to theinterior of the nozzle assembly 50, so that it can be discharged throughthe nozzle 60.

The mixer tube/diffuser assembly 52 is linked to the nozzle assembly 50by a link structure 82, for example comprising a set of link bars thatextend from the mounting portion 56 of the nozzle assembly to theupstream end of the mixer tube/diffuser assembly 52. This link structure82 can be permanently attached to the nozzle assembly 50 and the mixertube/diffuser assembly 52 for example by welding so that the twoassemblies 50,52 form a single component, or it can be designed to allowthe nozzle assembly 50 and the mixer tube/diffuser assembly 52 to beseparated. For example, the nozzle assembly 50 and the mixertube/diffuser assembly 52 may be connected by separable bolts.

The bars comprising the link structure 82 are spaced apart to provide anopening 84 through which a low pressure second fluid LP can flow fromthe second inlet pipe 42 into the nozzle discharge zone 70 downstream ofthe nozzle 60. The LP second fluid can then combine with the first fluiddischarged through the nozzle 60, and the combined first and secondfluids CF can then mix as they flow together through the mixertube/diffuser assembly 52 towards the outlet 48.

In use, a high pressure first fluid HP flows through the first inlettube 40 upstream of the nozzle assembly 50 and is discharged through thenozzle 60 into the low pressure nozzle discharge zone 70 immediatelydownstream of the nozzle 60. The nozzle 60 is constricted to increasethe velocity of the fluid as it is discharged from the nozzle. In thisway the potential (pressure) energy of the first fluid is converted tokinetic energy as the fluid emerges from the nozzle 60. This reduces thepressure at the low pressure nozzle discharge zone 70.

A low pressure second fluid LP passes through the second inlet pipe 42and is introduced into the low pressure nozzle discharge zone 70downstream of the nozzle 60. The second fluid is combined in the nozzledischarge zone 70 with the first fluid emerging from the nozzle 60 andthe first and second fluids are mixed within the mixing tube 66downstream of the nozzle 60 to form a combined fluid CF. The combinedfluid CF then passes through the expanding diffuser 68, where thevelocity of the combined fluid CF normalises and pressure recovery takesplace. Finally, the mixture of fluids exits the jet pump 26 at outlet48. The combined fluid CF at the outlet 48 will be at an intermediatepressure value that lies between the pressures of the HP and LP fluidsat the first and second inlets 40, 42.

In the present invention the HP and LP fluids are introduced into thejet pump through flanged inlets 40, 42, which are attached non-axiallyto the main body of the jet pump, typically either perpendicular to orat an acute angle to the longitudinal axis A of the jet pump. Thisarrangement leaves free the first end 32 of the jet pump (which underprevious designs would have carried the HP nozzle) and allows access tothe internal components 50, 52 of the jet pump without having to removespool pieces connected to the first and second ends of the jet pump. Thefirst end 32 of the housing 30 is blinded during the normal operation ofthe jet pump 26 by the blind flange plate 49, which can be removed toallow access to the internal components.

After removing the blind flange plate 49 from the flanged first end 32,the entire combined nozzle assembly 50 and mixing tube/diffuser assembly52 can be pulled out of the housing 30 as a single unit, without havingto remove any spool pieces from the first and second ends of the jetpump. The nozzle assembly 50 and/or the mixing tube/diffuser assembly 52can then be removed and replaced as required.

In order to be able to remove the nozzle assembly 50 and the mixingtube/diffuser assembly 52 as a single unit this assembly has thefollowing unique features.

The cylindrical section 74 has an opening 80 that faces the HP inletpipe 40 to allow the HP fluid to enter the opening 80 and pass throughthe nozzle assembly 50. The nozzle assembly 50 is equipped with a pairof O-ring seals 62, which enable it to isolate the HP inlet 40 of thejet pump from the LP inlet 42 and the mixing tube/diffuser assembly 52.The seals 62 are preferably mounted on the nozzle assembly 50 so thatwhen the nozzle assembly 50 is pulled out of the jet pump housing 30,the seals 62 are retrieved and can be replaced if needed.

The nozzle assembly 50 is linked to the pull out assembly 76 by thecylindrical section 74, wherein one end of the cylindrical section isattached to the body of the nozzle assembly 50 and the other end isattached to the pull out assembly 76. The cylindrical section 74 may bepermanently attached to the body of the nozzle assembly 50, for exampleby welding, or it may be removably attached, for example by respectivescrew threads.

The link structure 82 is preferably welded to the outside body of themixing tube/diffuser assembly 52. The bars comprising the link structure82 can be of flat plate type, curved plate type or L-shaped to add totheir stiffness if required. The cylindrical section 74 and the linkstructure 82 are strong enough to hold the mixing tube/diffuser assembly52 and the nozzle assembly 50 together during operation of the jet pump26 and also when the assemblies 50, 52 are pulled out of the housing 30when it is necessary to change the design of the internal components orto install new internals components. The link structure 82, which iswelded at one end to the nozzle assembly 50 and at the other end to themixing tube/diffuser assembly 52, can be made in two separate sectionsthat overlap one another and are bolted together to connect the nozzleassembly 50 and the mixing tube assembly 52. This feature also enablesthe two units (the nozzle assembly 50 and the mixing tube/diffuserassembly 52) to be separated from one another and replaced individuallyif needed after being pulled out or during transport.

The mixing tube/diffuser assembly 52 is held in a centralised positioninside the jet pump housing 30 by two sets of rings 72 that are weldedto the external surface of the mixing tube/diffuser assembly 52. Theserings 72 can be equipped with seals to prevent fluids from entering theannular space between the mixing tube/diffuser assembly 52 and thehousing 30. Alternatively, the rings 72 can be provided with weep holesor similar vent features if it is not necessary to seal the gap betweenthe mixing tube 52 and the housing 30. In this case the rings 72 onlyserve to hold the mixing tube/diffuser assembly in position and preventit from vibrating. If required, the annular space between the mixingtube/diffuser assembly 52 and the housing 30 can be filled with greaseto prevent the ingress of fluids flowing through the jet pump 26. Therings 72 also act as dampeners to prevent the mixing tube/diffuserassembly 52 vibrating during operation.

The pull-out end assembly 76 is equipped with an extension part 78. Thisextension part 78 is designed to allow an external pull out device to belocked onto it, enabling the pull out device 76 and the nozzle/mixingtube assembly 50, 52 to be removed and re-installed in the housing 30.There are many suitable methods for enabling the external pull outdevice to be locked onto the internals pull out end.

The blind flange plate 49 can be a standard blind flange, which isattached to the flange 36 at the first end 32 of the housing with bolts.Alternatively, the connection to the first end 32 of the housing can beof clamped type or of collet type, or any other connection mechanismavailable in the industry may be used as site conditions dictate. Thisalso applies to the connections provided at the first and second inletpipes 40, 42 and to the discharge flange 38 at the second end 34. Allthree types of connection, whether flanged, collet or clamp type, areindustry standard connectors which can be used depending on the pressurerating of the system or their use for onshore, offshore or subseaapplications.

Subsea Applications of the Jet Pumps

The combined nozzle assembly 50 and mixing tube/diffuser assembly 52described above is ideal for use in subsea applications, as this allowsthe entire set of internal components to be pulled out with the help ofa remotely operated vehicle (ROV) when needed without having todisconnect the inlet and outlet pipelines including the HP and LP inletlines. The jet pump in this case can be installed in horizontal orvertical mode depending on the details of the subsea module and featuresincluded to assist the ROV to lock onto the module and pull out theinternal components.

1. A jet pump including an elongate tubular housing that comprises alongitudinal axis, an upstream first end and a downstream second end, anozzle assembly and a mixing tube/diffuser assembly, said nozzleassembly and said mixing tube/diffuser assembly being removably receivedwithin the housing, a first inlet vent for a HP first fluid, a secondinlet vent for a LP second fluid and an outlet vent at the downstreamsecond end of the housing for the combined first and second fluids,wherein the first and second inlet vents extend non-axially through acircumferential wall of the tubular housing, and wherein the nozzleassembly and the mixing tube/diffuser assembly can removed from thehousing through the upstream first end thereof.
 2. A jet pump accordingto claim 1, wherein one or both of the first and second inlet ventsextend through a circumferential wall of the tubular housing at an angleθ relative to the longitudinal axis, where 0°<θ≦90°.
 3. A jet pumpaccording to claim 1, further including a removable closure member atthe upstream first end of the housing.
 4. A jet pump according to claim1, wherein the nozzle assembly and the mixing tube/diffuser assembly areinterconnected by a link assembly.
 5. A jet pump according to claim 4,wherein the link assembly is configured such that the nozzle assemblyand the mixing tube/diffuser assembly are separable.
 6. A jet pumpaccording to claim 1, further including a pull-out assembly connected tothe nozzle assembly for extracting the nozzle assembly and the mixingtube/diffuser assembly from the housing through the upstream first endthereof.
 7. A jet pump according to claim 6, wherein the pull-outassembly is separable from the nozzle assembly.
 8. A jet pump accordingto claim 6, further including a tubular sleeve element thatinterconnects the pull-out assembly and the nozzle assembly.
 9. A jetpump according to claim 8, wherein the tubular sleeve element includes afluid flow passageway configured to allow HP fluid to flow from thefirst inlet vent to the nozzle assembly.
 10. A jet pump according toclaim 1, wherein the first inlet vent extends through thecircumferential wall of the tubular housing upstream of the nozzleassembly.
 11. A jet pump according to claim 1, wherein the second inletvent extends through the circumferential wall of the tubular housingdownstream of the nozzle assembly and upstream of the mixingtube/diffuser assembly.
 12. A jet pump according to claim 2, furtherincluding a removable closure member at the upstream first end of thehousing.
 13. A jet pump according to claim 2, wherein the nozzleassembly and the mixing tube/diffuser assembly are interconnected by alink assembly.
 14. A jet pump according to claim 3, wherein the nozzleassembly and the mixing tube/diffuser assembly are interconnected by alink assembly.
 15. A jet pump according to claim 2, further including apull-out assembly connected to the nozzle assembly for extracting thenozzle assembly and the mixing tube/diffuser assembly from the housingthrough the upstream first end thereof.
 16. A jet pump according toclaim 3, further including a pull-out assembly connected to the nozzleassembly for extracting the nozzle assembly and the mixing tube/diffuserassembly from the housing through the upstream first end thereof.
 17. Ajet pump according to claim 4, further including a pull-out assemblyconnected to the nozzle assembly for extracting the nozzle assembly andthe mixing tube/diffuser assembly from the housing through the upstreamfirst end thereof.
 18. A jet pump according to claim 5, furtherincluding a pull-out assembly connected to the nozzle assembly forextracting the nozzle assembly and the mixing tube/diffuser assemblyfrom the housing through the upstream first end thereof.
 19. A jet pumpaccording to claim 7, further including a tubular sleeve element thatinterconnects the pull-out assembly and the nozzle assembly.
 20. A jetpump according to claim 6, wherein the first inlet vent extends throughthe circumferential wall of the tubular housing upstream of the nozzleassembly.
 21. A jet pump according to claim 20, wherein the second inletvent extends through the circumferential wall of the tubular housingdownstream of the nozzle assembly and upstream of the mixingtube/diffuser assembly.